Handbook of Functionalized Organometallics Applications in S

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13 Manganese Organometallics for the Chemoselective Synthesis of Polyfunctional Compounds
FG
Cl
1) Mn* (Rieke)
2) PhCOCl
5% CuI
FG = m-CF 3, p-F, p-Br, p-OAc
Scheme 13.30
Br
Scheme 13.31
O
FG
O 1) Mn* (Cahiez)
2) PhCOCl, 5% CuCl
O
71-84%
13.4.2
Manganese-Catalyzed Acylation of Grignard Reagents
Grignard reagents are readily acylated in the presence of a catalytic amount of
manganese chloride, in THF under very mild conditions (0 to 10 C), to give the
corresponding ketones in excellent yields (Scheme 13.32) [32]. A mechanistic
study evidenced that organomanganates are probably the effective intermediates
of this reaction. The scope of this procedure is very large; alkyl, alkenyl and arylmagnesium
reagents have been used successfully. The selectivity of the reaction
allows preparation of various functionalized ketones from carbocyclic acid chlorides
bearing functional groups (Cl, Br, esters, nitriles and even ketones).
RCOCl
Yield (%)
BuMgCl +
Cl
Scheme 13.32
O
58
Cl
( ) 3
Cl
O
71
RCOCl
Br
( ) 10
Cl
Ph
3% MnCl 4Li 2
THF, 0º to 10ºC
O
84
CN
( ) 6
Cl
O
O
( ) 4
83
76%
O
O
Bu R
O
OEt
O
Cl
O
( ) 5
91
O
Et